.
(ancient greek τετραπόδηs tetrapodēs, “four-footed”), or the tetrapods /ˈtɛtrəpɒd/,
.
(the superclass Tetrapoda comprises the first 4-limbed ‘vertebrates’ and their descendants, including the living and extinct ‘amphibians’, ‘birds’, ‘mammals’, ‘reptiles’, and some ancient, exclusively aquatic creatures such as the ‘Acanthostega’)
(‘Tetrapods’ evolved from the ‘lobe-finned fishes’ around 390 million years ago in the middle ‘Devonian Period’, with modern ‘tetrapod’ groups having appeared by the late ‘Devonian’, 367.5 million years ago)
(the specific aquatic ancestors of the ‘tetrapods’, and the process by which ‘land colonization’ occurred, remain unclear, and are areas of active research and debate among ‘palaeontologists’ at present)
(while most species today are ‘terrestrial’, the first ‘tetrapods’ were fully aquatic)
(‘amphibians’ today generally remain ‘semiaquatic’, living the first stage of their lives as fish-like ‘tadpoles’)
(‘amniotes’ evolved about 340 million years ago (crown amniotes 318 mya), and their descendants drove most ‘amphibians’ to extinction)
(one population of ‘amniotes’ diverged into ‘lizards’, ‘dinosaurs’, ‘birds’, and their relatives, while another diverged into ‘mammals’ and their extinct relatives)
(several groups of ‘tetrapods’, such as the ‘caecilians’, ‘snakes’, ‘cetaceans’, ‘sirenians’, and ‘moas’ have lost some or all of their limbs)
(in addition, many ‘tetrapods’ have returned to partially aquatic or fully aquatic lives throughout the history of the group (modern examples of fully aquatic ‘tetrapods’ include ‘cetaceans’ and ‘sirenians’))
(the first returns to an ‘aquatic lifestyle’ may have occurred as early as the ‘Carboniferous Period’, whereas other returns occurred as recently as the ‘Cenozoic’, as in ‘cetaceans’, ‘pinnipeds’, and several modern ‘amphibians’)
(the change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known)
(it is also becoming increasingly well-understood as a result of more transitional fossil finds and improved ‘phylogenetic analysis’)
.
.
.
.
.
.
💕💝💖💓🖤💙🖤💙🖤💙🖤❤️💚💛🧡❣️💞💔💘❣️🧡💛💚❤️🖤💜🖤💙🖤💙🖤💗💖💝💘
.
.
*🌈✨ *TABLE OF CONTENTS* ✨🌷*
.
.
🔥🔥🔥🔥🔥🔥*we won the war* 🔥🔥🔥🔥🔥🔥